Conventional disk drives with magnetic media organize data in concentric tracks that are spaced apart. The concept of shingled writing is a form of perpendicular magnetic recording and has been proposed as a way of increasing the areal density of magnetic recording. In shingle-written magnetic recording (SMR) media a region (band) of adjacent tracks are written so as to overlap the previously written track. The shingled tracks must be written in sequence unlike conventionally separated tracks, which can be written in any order. The tracks on a disk surface in an SMR drive are organized into a plurality of shingled regions (also called I-regions) which can be written sequentially from an inner diameter (ID) to an outer diameter (OD) or from OD to ID. Once written in the shingled structure, an individual track cannot be updated in place, because that would overwrite and destroy the overlapping tracks. Shingle-written data tracks, therefore, from the user's viewpoint are sometimes thought of like append-only log structures. To improve the performance of SMR drives, a portion of the media is allocated to so-called “exception regions” (E-regions) which are used as staging areas for data which will ultimately be written to an I-region. The E-region is sometimes referred to as an E-cache. E-regions can optionally be shingled as well.
In SMR drives the effective writing width of the write head is wider than the effective reading width of the read head. The width of the final data track in a region is typically made adjustable by the parameter settings of the SMR drive. For example, the track width can be made wider by having less overlapping of the next track. To maximize data storage capacity, narrower tracks are desired, but tracks should not be made so narrow that data is corrupted during the write of the adjacent shingled track.
The temperature of the magnetic media at the time of data writing affects the permeability of the magnetic media. At higher magnetic media temperature, the same write head magnetic field will write a wider data track because the switching threshold of magnetic media grains is lowered. Similarly a lower magnetic media temperature requires a stronger magnetic field to switch polarity of the grains so the same magnetic field generated by the write head will result in a narrower track width.
Thermal-assisted recording (TAR) uses a write head with a heater element for temporarily heating the magnetic media to enable smaller magnetic media grains to be written with a weaker magnetic field. However, the power and/or focus of the heater element can change with time or deterioration of the write head and alter the temperature of the media during write operations.
Changes in environmental temperature can cause the magnetic write width (MWW) to change in shingled magnetic recording (SMR). The magnetic data width when written at a low temperature can be narrower than desired track width. Additional complications arise when write heads with thermal assistant elements (e.g. TAR and microwave-assisted magnetic recording (MAMR)) are used since the outputs of these elements can deteriorate with age.
U.S. Pat. No. 7,898,755 to Mochizuki, et al. (Mar. 1, 2011) describes a method for measuring write width and/or read width of a composite magnetic head. A write sensitive width is calculated by writing test data by moving the write head in a radial direction of a magnetic recording medium at a designated speed to obliquely cross a designated track or a track adjacent to the designated track. Then reading the test data recorded in the track obliquely by a read head to obtain a read characteristics profile of a read voltage with respect to the track scanning time. A moving distance is obtained in the radial direction of the head by multiplying the test data scanning time of the read head with the designated moving speed.
U.S. Pat. No. 7,102,838 to Kim, et al. (Sep. 5, 2006) describes a method of optimizing a recording current in consideration of operating temperatures of a hard disk drive and a method of setting a recording density in consideration of tracks per inch (TPI) or adjacent track erasure (ATE) characteristics. Kim describes the conventional method of optimizing the write current or an overshoot current according to the temperature of the hard disk drive. The write current or the overshoot current is increased at low temperatures. The rate of errors under a test condition corresponding to the operating temperature of a hard disk drive is measured, while changing a recording parameter. The recording parameter value corresponding to a smallest rate of errors is selected.
U.S. patent application 20100277827 by Wood, et al. (Nov. 4, 2010) describes adjusting the amount of current to a magnetic-recording head of the HDD to cause a change in the strength of a magnetic write field produced by the magnetic-recording head in response to a determination that a present position of the magnetic-head head is not in a desired position. If the magnetic-recording head is further away from an edge of a current track being written than desired, the current to the magnetic-recording head is increased to cause an increase in the strength of the magnetic write field. In one embodiment, a laser is directed at the location on the surface of the disk to assist the writing process. This gives control over the temperature and the size of the heated area. Wood, et al. notes the relationship between the temperature of the surface of the magnetic-recording disk and the strength of the magnetic write field required to write to the heated portion of the magnetic-recording disk.
In U.S. Pat. No. 6,611,395 to Chainer, et al. (Aug. 26, 2003) the concept of adaptive track density in servowriting process for a non-SMR disk drive is described. The servowriting occurs as part of the initial manufacturing process and is not used to dynamically adjust to field conditions such as the temperature of the drive. In Chainer's method the servo-track pitch for each magnetic disk surface in a hard drive can be adaptively adjusted to take into account static variations in magnetic media characteristics, as well as, actual effective write and read head dimensions. The track pitch can also vary among separate bands of data tracks on a single side of a single disk.
U.S. Pat. No. 6,437,947 to Uno (Aug. 20, 2002) describes variations in the overlapping region of two adjacent data tracks based on geometry of disk components. Signals are recorded on and reproduced from a magnetic disk by a head with an azimuth angle which changes depending on a radial position on the magnetic disk. The magnetic disk includes a first recording region having tracks recorded with an azimuth angle less than or equal to a predetermined value, a second recording region having tracks recorded with an azimuth angle greater than the predetermined value, and an overlapping region in which two mutually adjacent tracks overlap in a radial direction of the magnetic disk, where a track pitch of the tracks within the first recording region is different from a track pitch of the tracks within the second recording region.